The main objective of this study was to determine the effect of aggregate gradation (AG) on the volumetric parameters (VPs) and rutting performance (RP) of asphalt concrete (AC) mixtures. The boundary sieve (BS) between fine and coarse aggregates was 2.36 mm size, and 15 gradation curves of three nominal maximum aggregate sizes (13.2, 19.0, and 26.5 mm) were designed based on the percentage passing of the BS. A vibrating compaction test of coarse aggregates, Marshall compaction and wheel-tracking tests of AC mixtures with various gradations were conducted. It was found that AG had crucial effects on the VPs and RP of AC mixtures. The AC mixture can be designed as a skeletal dense structure provided that the percentage passing of the BS is appropriate. More notably, AC mixtures with a skeletal dense structure showed the best rutting resistance performance. Therefore, it is important to optimize AG for enhancing the high-temperature RP of AC mixtures.

With the advancement of intelligent compaction technology, real-time quality control has been widely investigated on the subgrade, while it is insufficient on asphalt pavement. This paper aims to estimate the real-time compaction quality of hot mix asphalt (HMA) using an artificial neural network (ANN) classifier. A field experiment of HMA compaction was designed. The vibration patterns of the drum were identified by using the ANN classifier and classified based on the compaction levels. The vibration signals were collected and the degree of compaction was measured in the field experiment. The collected signals were processed and the features of vibration patterns were extracted. The processed signals were tagged with their corresponding compaction level to form the sample dataset to train the ANN models. Four ANN models with different hidden layer setups were considered to investigate the effect of hidden layer structure on performance. To test the performance of the ANN classifier, the predictions made by ANN were compared with the measuring results from a non-nuclear density gauge (NNDG). The testing results show that the ANN classifier has good performance and huge potential for estimating the compaction quality of HMA in real-time.

The research incorporates the technology of warm mix asphalt into asphalt rubber (forming into warm asphalt rubber) and evaluates the performance of warm asphalt rubber (WAR) binders. Crumb rubber modifiers (CRMs) of three particle sizes and one warm asphalt additive (WAA) are employed, and an orthogonal diagram is used to arrange the tests. The analysis shows that the bigger particle size and content of CRM all have positive effects on softening point, penetration index(PI), viscosity, temperature susceptibility described by viscosity, and low temperature property of WAR. But WAA content only produces positive impacts on softening point and PI; it cannot dramatically reduce the viscosity at high temperatures, and cannot improve the low temperature property of WAR. So employing WAA to reduce energy consumption for CRM-asphalt producing might be invalid.

Stone mastic asphalt (SMA) is the most widely adopted asphalt mixture on highway pavement in China. However, the cost of SMA is rising continually due to the increasing shortage of high-quality basalt aggregate. On the other hand, China’s steel slag and reclaimed asphalt pavement (RAP) stock is abundant, and steel slag has excellent strength and wear-resistant performance, which can fully or partially replace part of the basalt aggregate. The content of asphalt may be increased due to the porosity of the steel slag. If fine RAP rich in asphalt is also used for SMA, it can partially fill the voids of steel slag and reduce the amount of new asphalt and fine aggregate. For this objective, SMA 13 was designed with two particle sizes of coarse steel slag aggregate (5–10 mm, 10–15 mm) and one fine RAP (0–5 mm), named SR-SMA. The fundamental pavement performance of SR-SMA was evaluated through a wheel-tracking test, low-temperature beam bending test, freeze–thaw indirect tensile test, and four-point bending fatigue test. For comparison, the mix design and performance tests of two SMAs involving coarse steel slag and fine basalt aggregate (named SB-SMA), and coarse and fine basalt aggregates (named B-SMA), respectively, were conducted. The results indicated that SR-SMA (dynamic stability of 4865 passes/mm) shows the best rutting resistance, followed by SB-SMA (dynamic stability of 4312 passes/mm), and B-SMA (dynamic stability of 4135 passes/mm) comes in last. Additionally, the dynamic stability values of three SMAs have significant differences. SR-SMA has better low-temperature cracking resistance with a failure strain of 3150 με, between SB-SMA and B-SMA (failure strain values are 4436, 2608 με). Compared to B-SMA and SB-SMA, the moisture stability of SR-SMA is relatively poor but meets Chinese specification. While the fatigue resistance of SR-SMA is the worst among three SMAs, their differences are insignificant. Furthermore, SR-SMA reduces material cost by approximately 35% per ton compared to conventional B-SMA. Overall, SR-SMA is cost-effective and can be used as an alternative material to traditional B-SMA.

2.36 mm size was used as boundary sieve between coarse and fine aggregates, and five grading curves of three nominal maximum aggregate sizes (13.2, 19.0, and 26.5 mm) were respectively designed according to the percentage passing of the boundary sieve. The effect of various gradations on the key volumetric parameters and high temperature rutting resistance performance of asphalt concrete (AC) mixtures were studied through Marshall compaction test and wheel tracking test. The results showed that aggregate gradation has significant effect on the volumetric parameters and high temperature performance of three kinds of AC mixture. The percentage of voids in mineral aggregate (VMA) decreases first then increases with the increase of the passing percentage of the boundary sieve and shows a parabola going upwards, while the percentage of air voids (VV) decreases monotonically and tends to be constant. The values of dynamic stability (DS) increase first then decrease with the increase of the passing percentage of the boundary sieve, which present parabola going downwards. It can be inferred from the critical percentage passing corresponding to the minimum of VMA that the aggregate structure is in the densest state and the value of DS is also maximum, which prove that AC mixture with skeleton dense structure has the best rutting resistance performance.

Stone matrix asphalt and asphalt concrete mixture with 13.2 mm nominal maximum aggregate size (named SMA13 and AC13, respectively) are widely used in the surface course of asphalt pavement in China. Generally, the pavement performance of SMA13 is superior to that of AC13, while the cost of the former is significantly higher than that of the latter. The objective of this paper was to develop a new hot mix asphalt (named SMAC13) whose performance and cost are between SMA13 and AC13. A boundary sieve size (BSS) of 2.36 mm was selected between fine and coarse aggregates. Based on the union set of aggregate gradation ranges of SMA13 and AC13, the family of gradation curves in the forms of S shapes were designed in terms of the BSS passing rate. According to the evaluation of the skeleton interlock of coarse aggregate of the gradation curve family, the aggregate gradation range of SMAC13 was determined. Also, the performance of three kinds of asphalt mixtures were compared through laboratory tests. The results indicated that SMA13 shows the best rutting resistance, followed by SMAC13 then AC13, while in terms of low-temperature performance in resistance to cracking, the sequence is SMAC13, AC13, and SMA13. The sequence of water stability is AC13, SMAC13, and SMA13. Furthermore, the cost of SMAC13 is 25% less than that of SMA13. Therefore, SMAC13 can be used as an alternative for the surface course of asphalt pavement in terms of performance and cost.